EP2891771B1 - Method for refining crude lignite - Google Patents

Description

The invention relates to a method for refining raw lignite comprising pre-comminuting the humidified raw lignite as well as grinding and drying directly downstream of the pre-comminution to dry lignite, steam being removed from a coupled power plant process with at least one steam generator and being used at least partially to dry the mine-moist raw lignite.

Refining lignite in the sense of the present invention means at least drying and grinding the lignite for the purpose of producing a marketable product that can be used outside the power plant process. Refinement can include at least the production of a dried, powdery or granular end product, which is subjected to thermal recycling in a power plant or a further refinement for the enrichment of carbon in the end product. As a further refinement step, for example, the production of hearth furnace coke, liquefaction, gasification or the production of fuel pellets can be provided.

Mine-moist raw lignite in the sense of the present invention is to be understood as the mined and not prepared raw lignite, which can have a moisture content between 40% by weight and 60% by weight, depending on the conditions of the deposit or storage time before refining.

When lignite is converted into electricity, the raw lignite is usually fed to a beater mill which has been rendered inert with flue gas. The raw lignite is crushed in the mill. The flue gas is used to dry the moist coal and transports the lignite dust generated as a carrier gas through a classifier to the boiler's burner.

The refining of lignite, on the other hand, requires a possibly multi-stage grinding and separate drying of the raw lignite in a separate drying unit. Tube dryers, fluidized bed dryers or roller bowl mills are used as drying units. When tube dryers and fluidized bed dryers are used as drying units, multi-stage pre-comminution and / or grinding of the raw lignite is usually provided. In particular, fluidized bed dryers can only be operated with a relatively narrow feed belt, since otherwise the fluidized bed would collapse. The operation of tube dryers is energy-intensive. These are usually operated with steam from a coupled power plant process. The specific steam volume required to operate a tube dryer is approximately 1.35 kg steam per kilogram of raw coal. The situation is similar with the operation of a fluidized bed dryer, the steam consumption of which, based on the raw coal used, is about 1.2 kg of steam per kilogram of raw coal. Finally, in particular the multi-stage grinding and classification of the raw coal fed to the fluidized bed dryer is expensive in terms of equipment.

In principle, the pit-moist raw lignite can be dried and ground in roller bowl mills inertized with flue gas, although the investment costs for roller bowl mills are considerable.

From the WO 2012/133549 A1 a method for processing raw lignite is known, in which the raw lignite is first fed to a comminution unit and the comminuted raw lignite is then fed into a fluidized bed dryer.

From the DE 150 520 A1 a method and a device for operating a gas turbine are known. From the DE 10 2007 023 336 A1 A method for operating a steam turbine power plant and a device for generating steam are known.

The invention is therefore based on the object of a method for refining raw lignite comprising the comminution and drying of the raw lignite to provide dry lignite, which requires energy-efficient drying with relatively little equipment.

The object is achieved with the features of claim 1. Advantageous refinements of the invention result from the subclaims.

A method according to the invention comprises pre-comminution of the mine-moist raw lignite as well as drying to dry lignite, which is preferably immediately downstream of the pre-comminution, steam being extracted from a coupled power plant process with at least one steam generator and this steam being used at least partially for drying the mine-moist raw lignite, the method being used comprises grinding and drying in a single process step, preferably fine grinding and drying in a single process step, the raw lignite still pre-crushed from the mine being crushed as ground material by means of at least one steam jet from the steam generation, which is introduced into a ground material bed fluidized with steam, is crushed and broken . According to the invention, this combines fine grinding and drying in one process step, which results in a considerable energetic optimization of the finishing process. According to the invention, it is provided that the raw lignite itself is used as grinding media within a correspondingly configured unit. The steam jet entering the regrind bed, comprising the pre-broken or pre-comminuted raw lignite as regrind, interacts with the fluid bed surrounding it in such a way that an exchange of impulses takes place between the steam jet and the regrind, which leads to comminution of the regrind and at the same time to drying it in the Steam atmosphere leads. The steam jet, together with part of the regrind, is accelerated into the fluidized regrind bed and this is done in such a way that particle collisions within the regrind bed occur. The individual lignite particles are exposed to an impact, which leads to comminution without the use of grinding media or impact internals within the unit concerned. Thereby several Steam jets introduced into the regrind bed in opposite directions, for example in such a way that steam jets meet.

The comminution and drying can be carried out in at least one, preferably in a plurality of hydraulic jet mills connected in parallel, preferably in fluid bed counter-jet mills. In a fluidized bed counter-jet mill, at least two or more steam jets, each loaded with regrind, are directed towards one another in order to achieve particle collisions to the greatest extent possible.

Such comminution is particularly advantageous if the upgrading process is coupled to a power plant process, in which case appropriately conditioned steam from the power plant process or steam generation process is available.

In the method according to the invention it can be provided that a part of the dry brown coal is thermally utilized in the power plant process, the rest of the power plant process preferably being operated with raw brown coal as fuel.

The steam can be introduced into the regrind bed, for example, at a temperature of between 180 ° C. and 330 ° C., preferably with a temperature between 200 ° C. and 300 ° C. and a steam pressure between 4 bar and 6 bar, preferably with a steam pressure of 5 bar will.

In a particularly preferred variant of the method according to the invention, both water and volatile constituents of the raw brown coal, such as methane, are expelled as fuel gas from the raw brown coal during the drying, the fuel gas being stored and / or separately thermally utilized. The so-called volatile constituents or volatile gaseous constituents in the sense of the present invention are to be understood exclusively as hydrocarbons, but not the roughly capillary bound water of the raw lignite.

A further process variant according to the invention provides that the grinding and drying take place in two stages, the grinding and drying taking place in one stage by means of at least one steam jet at a first low temperature and in a second stage using at least one steam jet at a second higher temperature, For example, the low temperature may be on the order of 200 ° C, whereas the higher temperature may be on the order of 300 ° C.

When a steam jet is introduced at a temperature of approximately 200 ° C. and a pressure of approximately 5 bar, the ground material is only finely comminuted and dried, the dried ground material then preferably having a residual water content of approximately 2% by weight to 4% by weight. can have. In this case, the product obtained still contains significant amounts of volatile gaseous components.

In a second stage of grinding and drying, for example, steam can be supplied at a temperature of approximately 300 ° C., which results in the volatile gaseous components being expelled from the raw lignite. These volatile constituents can, for example, be stored separately and / or sent for thermal recycling.

It when the second stage of fine grinding and drying is operated depending on the load of the steam generator is particularly advantageous. For example, during low-load times of the power grid, it can be provided that the steam generator is supplied with a portion of the dry lignite from which the volatile constituents have already been driven off. In this case, the volatile constituents can be compressed as fuel gas and fed to a natural gas network or a natural gas storage facility. In this case, in order to expel the volatile constituents in a second stage of fine grinding and drying, steam with a relatively high energy content is required, which is no longer available to generate electricity at the turbine power plant.

At high load times, only a single stage of grinding and drying can be operated with steam of a first lower temperature, so that the steam higher energy content is available on a turbine and ultimately also on a downstream generator for power generation.

The partial stream of dry lignite not supplied for thermal utilization can be coked, for example, in a further upgrading step to hearth furnace coke if and to the extent that this dry lignite still contains gaseous volatile constituents. If the volatile components are completely expelled in the second stage of fine grinding, the finished, dried product is already in the form of a high-quality coke.

Tapped steam from a turbine of the coupled power plant process is preferably provided as steam. For example, the steam can be drawn off between the low-pressure part and the medium-pressure part of a three-stage turbine.

The invention is explained below with reference to an embodiment shown in the drawings.

Figur 1:

ein Verfahrensfließbild einer ersten Variante des erfindungsgemäßen Verfahrens und

Figur 2:

ein Verfahrensfließbild einer zweiten Variante des Veredelungsverfahrens gemäß der Erfindung.

Show it:

Figure 1:

a process flow diagram of a first variant of the method according to the invention and

Figure 2:

a process flow diagram of a second variant of the finishing process according to the invention.

Reference is first made to the Figure 1 .

In Figure 1 A lignite refinement coupled with a power plant process is shown, the refinement comprising a pre-comminution 1 and a fine comminution with drying 2.

In the simplest case, the pre-shredding 1 for raw lignite from the mine can only lead to a pre-crushing of mined mine moisture Include raw lignite using conventional crushers / pre-shredders. For example, the raw lignite may have been pre-crushed to a grain size of ≥ 0 mm and ≤ 10 mm. The pre-crushed raw lignite can have a moisture content of 54% by weight, for example. The moisture content is only given here as an example, naturally the moisture content of the raw lignite can fluctuate depending on the storage conditions and deposit conditions.

As a fine comminution and drying 2, for example, an arrangement of parallel fluidized bed jet mills is provided, in which the feed grain from 0 mm to 10 mm to a target grain of ≤ 1 mm with simultaneous drying to a moisture content of about 2% by weight to 3% by weight. is obtained.

A hydraulic jet mill suitable for carrying out the method can comprise, for example, a regrind in which several jet tubes are immersed. The jet pipes both introduce steam and, if appropriate, introduce regrind that has previously been withdrawn from the regrind bed or a regrind inlet. A regrind can be discharged, for example, via a classifier arranged inside the regrind room.

A partial stream A of the ground material stream discharged from the fine comminution and drying 2 in the form of dry brown coal is fed to a steam generator 3, which is designed, for example, as a boiler which is essentially fired with raw brown coal. It can be provided, for example, that the steam generator 3 is fired at 75% with raw lignite and 25% with dry lignite. The superheated steam generated in the steam generator 3 drives a turbine 4, which in turn drives a generator 5, which feeds into a power grid 6. Another partial stream B of dry lignite is fed to a second upgrading stage 7, the goal of which is the production of a high-quality, marketable fuel. Coking, gasification or liquefaction of the lignite can, for example, be provided as the second upgrading stage 7.

To operate the fine comminution and drying 2, a partial stream of steam C is withdrawn from the turbine 4. According to the invention, this partial stream steam C is introduced as a steam jet into the drying units provided there. In addition, this partial stream steam C is used for fluidizing the regrind bed provided within the drying units. The steam is drawn off between the low-pressure part and the medium-pressure part of the turbine 4 at a pressure of about 5 bar at a temperature of about 200 ° C., about 0.95 kg of steam being required per kilogram of raw brown coal used as regrind. The vapor stream D drawn off from the fine comminution and drying 2, which is obtained in the course of drying the raw lignite to dry lignite, is condensed in a vapor condenser 8, the resulting heat of condensation, for example, for preheating the boiler feed water of the steam generator 3 or in a separate ORC process (Organic Rankine Cycle) is used.

A variant of this method is in Figure 2 shown, where the same components and the same mass flows are provided with the same names.

In the Figure 2 The variant of the method according to the invention shown differs essentially from that in FIG Figure 1 variant shown that the fine comminution and drying 2 is operated in one or more stages, but with a partial stream steam C, which has a higher energy content or a higher temperature, namely about 300 ° C at a pressure of about 5 bar. When operating a hydraulic jet mill with steam at a temperature of about 300 ° C at about 5 bar pressure, both water and the gaseous volatile constituents of the raw lignite are expelled from the latter during comminution, in such a way that almost 100% of the raw lignite is contained Moisture is removed. When 100% raw lignite is used, about 54% by weight of water and 23.5% by weight of methane are obtained. A coke-like product with an increased carbon content is obtained as the finished product from the fine comminution and drying 2, of which a partial stream A in the steam generator 3 can be thermally utilized, whereas another partial stream B is obtained as a finished product. The vapors D from the fine grinding and drying 2 can as in the previously described method variant, are condensed in the vapor condenser 8 for the purpose of utilizing waste heat.

The resulting methane E is first cleaned in a filter 9 and then fed into a natural gas network 11 via a compressor 10.

The fine comminution and drying 2 can comprise two grinding and drying stages, it being possible in a first stage to provide fine comminution and drying or grinding and drying with steam of lower energy content. This can take place, for example, during peak periods of the power grid, since in this case the maximum amount of steam must be available at the turbine 4. At low load times, a second grinding and drying stage can be provided, which is operated with steam having a higher energy content, steam then being able to be drawn off from the turbine 4 at a temperature of approximately 300 ° C. Only in this load case would methane E be driven out of the raw lignite and be used separately as fuel gas.

Reference symbol list

1

Pre-shredding

2nd

Fine crushing and drying

3rd

Steam generator

4th

turbine

5

generator

6

power grid

7

second finishing stage

8th

Vapor condenser

9

filter

10th

compressor

11

Natural gas network

A

Dry lignite

B

Dry lignite

C.

steam

D

Brothers

E

methane

Claims (9)

1. Method for refining pit-moist raw lignite, comprising pre-comminution (1) of the pit-moist raw lignite as well as grinding and drying into dry lignite immediately downstream of the pre-comminution (1), steam being removed from a coupled power plant process by means of at least one steam generator (3) and at least partially used to dry the pit-moist raw lignite, the grinding and drying being executed in one method step, the still pit-moist pre-crushed raw lignite being fed as ground material into a fluidized bed of ground material and being finely comminuted and dried within the bed of ground material by means of at least one steam jet, the raw lignite being comminuted within the bed of ground material by means of a plurality of contradirectionally oriented steam jets, characterized in that at least parts of the raw lignite are fed into the ground material by means of the steam jets.
2. Method according to claim 1, characterized in that the fine comminution and drying is carried out in at least one hydraulic jet mill, preferably in a plurality of hydraulic jet mills connected in parallel, preferably in fluidized bed opposed jet mills.
3. Method according to either claim 1 or claim 2, characterized in that the at least one steam jet is introduced into the bed of ground material at a temperature of between 180°C and 330°C and a steam pressure of between 4 bar and 6 bar.
4. Method according to any of claims 1 to 3, characterized in that, during drying, water and volatile gaseous components such as methane are expelled from the raw lignite as fuel gas, the fuel gas being stored and/or separately thermally utilized.
5. Method according to any of claims 1 to 4, characterized in that a portion of the dry lignite is thermally utilized in the power plant process, which is otherwise preferably operated using raw lignite as fuel.
6. Method according to either claim 4 or claim 5, characterized in that the fine comminution and drying is carried out in two stages, the fine comminution and drying (2) being carried out by means of at least one steam jet at a first lower temperature in a first stage and by means of at least one steam jet at a second higher temperature in a second stage.
7. Method according to claim 6, characterized in that the second stage of the fine comminution and drying (2) is carried out depending on the load of the steam generator (3).
8. Method according to any of claims 1 to 7, characterized in that the waste heat from the fine comminution and drying (2) of the raw lignite is used in the generation of steam.
9. Method according to any of claims 1 to 8, characterized in that bleed steam from a turbine (4) of the coupled power plant process is provided as steam.

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